The objective of the proposed research is to investigate the relationship between steroid hormone action at the cellular and subcellular level within the central nervous system and the hormonal regulation of behavior. More specifically, the experiments to be described are concerned with the role of neural receptors for one class of steroid hormones, the progestins, in the mediation of female sexual behavior. After a sufficient (24-48 hr) period of estrogen priming, an injection of progesterone synergizes with estrogen to induce high levels of sexual receptivity in female rodents. This same period of estrogen priming also induces the synthesis of progestin receptors in the hypothalamus, a brain region known to be intimately involved in the activation of female sexual behavior. These observations have led to the proposal that the estrogen-induced progestin receptors are intracellular mediators of progesterone's facilitation of sexual receptivity. However, a 24-48 hr priming with estrogen is also required before progesterone can facilitate the release of gonadotropins (LH and FSH), another function which is regulated primarily by the hypothalamus. The proposed research will therefore utilize neonatal gonadectomy and androgen treatment to produce animals in which the control systems for female sexual behavior and gonadotropin release have been dissociated. The ability of estrogen to induce progestin receptor synthesis in these animals will then be measured and correlated with the capacity of estrogen plus progesterone to facilitate female sexual responses or gonadotropin release. By dissociating the control of behavior and pituitary hormone release, it should be possible to determine whether estrogen-inducible hypothalamic progestin receptors mediate progesterone's effects on behavior, gonadotropin secretion, or both.